A Network Science Approach for Determining the Ancestral Phylum of Bacteria

Perhaps the most important organizing principle in biology for bac- teria is the tree of phyla. It represents the evolution of bacteria now living in virtually every environment. The availability of whole genome sequences has provided the opportunity to reconstruct a comprehensive view of the tree and to trace the shared ancestry among all bacteria that have been sequenced. However, most exist- ing research has presented the tree of phyla without considering the ancestral phylum. The objective of this study is to fi nd the ancestral phylum using a network science approach and exploiting the availability of a rich dataset of genomes. For the analysis, a network representing 210 organisms is created by clustering more than 700,000 protein sequences for 28 recognized phyla. A network of phyla is then extracted from the results which is examined using a breadth-fi rst search algorithm and centrality measures to create a rooted tree from which the likely ancestral phylum is identified.